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- Budhavant, Krishnakant, et al.
(författare)
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Changing optical properties of Black Carbon and Brown Carbon aerosols during long-range transport from the Indo-Gangetic Plain to the equatorial Indian Ocean
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Atmospheric aerosols strongly influence the global climate by their light absorption (e.g., black carbon, BC, brown carbon, BrC) and scattering (e.g., sulfate) properties. This study presents simultaneous measurements of ambient aerosol light absorption properties and chemical composition from three large-footprint South Asian receptor sites during the South Asian Pollution Experiment (SAPOEX) in December 2017 - March 2018. The BC mass absorption cross-section (BC-MAC678) values increased from 3.5 ± 1.3 at the Bhola Climate Observatory-Bangladesh (i.e., located at exit outflow of Indo-Gangetic Plain) to 6.4 ± 1.3 at the two regional receptor observatories at Maldives Climate Observatory-Hanimaadhoo (MCOH) and Maldives Climate Observatory-Gan (MCOG), an increase of 80%. This likely reflects a scavenging fractionation resulting in a population of finer BC with higher MAC678 having higher longevity. At the same time, the BrC-MAC365 decreased by a factor of three from the IGP exit to the equatorial Indian Ocean, likely due to photochemical bleaching of organic chromophores. The high chlorine-to-sodium ratio at the near-source-region BCOB suggests a significant contribution of chlorine from anthropogenic activities. This particulate Cl- has the potential to convert into Cl-radicals that can affect the oxidation capacity of the polluted air. Moreover, Cl- is shown to be near-fully consumed during the long-range transport. The results of this synoptic study over the large South Asian scale contribute rare observational constraints on optical properties of ambient BC (and BrC) aerosols over regional scales away from emission sources. It also contributes significantly to understanding the ageing effect of the optical and chemical properties of aerosols as the pollution from the Indo-Gangetic Plain disperses over the tropical ocean.
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- Holmstrand, H., et al.
(författare)
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Origin of PCDDs in ball clay assessed with compound-specific chlorine isotope analysis and radiocarbon dating.
- 2006
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 40:12, s. 3730-5
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Tidskriftsartikel (refereegranskat)abstract
- Polychlorinated dibenzo-p-dioxins (PCDDs) of high concentrations in a ball clay deposit from the Mississippi Embayment were found to be consistent with a natural abiotic and non-pyrogenic origin by investigation with bulk radiocarbon analysis, compound-specific chlorine isotope analysis (CSIA-delta37Cl) of octachlorodibenzo-p-dioxin (OCDD), and black carbon (BC) analysis. The conventional radiocarbon date of total organic carbon from a depth of approximately 10 m in three parallel cores ranged from 14 700 years to >48 000 years, indicating that the strata with elevated levels of PCDDs have remained isolated from recent anthropogenic input in these >40 Ma old clay sediments. The CSIA-delta37Cl of OCDD yielded a delta37Cl of -0.2 per thousandth, which is significantly higher than the postulated range for biotic chlorination by chloroperoxidase enzymes, -11 to -10 per thousandth, and falls within the known range for abiotic organochlorines, -6 to +3 per thousandth. The absence of correlations between concentrations of PCDDs and corresponding pyrogenic black carbon (BC), together with estimations of BC sorptive loadings and the absence of polychlorinated dibenzofurans (PCDFs), suggest that vegetation fires did not form these ball-clay PCDDs. Results from this study indicate that the high levels of the toxic and carcinogenic PCDDs found in kaolinite-bearing clays may result from natural abiotic formation via in situ surface-promoted reactions on the clay mineral, including a so-far unknown organic precursor, rather than being the result of anthropogenic contamination.
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- Norström, Elin, et al.
(författare)
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Late Quaternary vegetation dynamics and hydro-climate in the Drakensberg, South Africa
- 2014
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 105, s. 48-65
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Tidskriftsartikel (refereegranskat)abstract
- Abstract A multi-proxy study of a sediment sequence from Braamhoek wetland, covering the last c. 16,000 years, reveals a record of regional climate and vegetation dynamics in the Drakensberg region, South Africa, including signals from both the organic sediment fraction (fossil pollen, charcoal, n-alkane abundance, n-alkane δ13C, TOC) and the inorganic fraction (mineral magnetic properties). The reconstruction, supported by a robust chronology, indicates two major periods of increased regional wetness during the late Pleistocene to early Holocene phase (c. 13,800–12,600 cal yr BP; c. 10,200–8500 cal yr BP) and one during the late Holocene (c. 2000 cal yr BP to present). Drier conditions are recorded during the Younger Dryas (c. 12,600–11,300 cal yr BP) and mid-Holocene (c. 7000–2000 cal yr BP). A major decline in fynbos vegetation during the early Holocene suggests a shift towards warmer temperatures and possibly towards less pronounced winter rains in eastern South Africa from c. 8500 cal yr BP. Comparison with records from interior of South Africa show relatively high inter-site variability, however, the Braamhoek moisture proxies do co-vary with the speleothem isotope records from Makapansgat, suggesting a similar hydro-climate evolution in eastern and interior parts of the summer rainfall region during the studied period. On multi-millennial time scales, an inverse hydro-climatological pattern is evident between these two South African records and reconstructions from tropical locations in southeast Africa. Such a rainfall dipole between eastern tropical and southern Africa, has previously been identified on shorter time scales, i.e. on inter-annual to millennial scales. The Braamhoek study suggests that a similar dipole pattern is acting also on a multi-millennial perspective. These long-term precipitation anomalies are tentatively coupled to teleconnections from multi-millennial changes in the dynamics of the Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO).
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